The invention relates to an injector apparatus of the kind having a constriction at the beginning of a mixing section disposed in a mixing pipe, particularly for aerating suspensions for the flotation of solid matter contained therein.
An injector apparatus of this kind is disclosed in German Pat. No. 2,634,496. In this apparatus, suspension mixed with air is supplied to the flotation tank through an injector nozzle with a mixing pipe adjoining it in such a way that fine air bubbles are distributed through the suspension, bringing about a flotation effect. There is further disclosed in German Pat. No. 2,634,496, general-purpose injectors for aerating liquids wherein a drive jet of suspension is supplied to a mixing pipe through a nozzle. In this arrangement there is a deflecting element in the mixing pipe, specifically constructed as a body of rotation. In another version of the device as described in this German patent, the drive jet is distributed over a plurality of mixing sections which taper toward their outlet ends.
In another known arrangement according to Austrian Pat. No. 342,528, there is an injector with a Laval nozzle with a central air supply pipe opening into its narrowest point.
An object of the present invention is to provide an injector apparatus in which there is a high flow rate of air with economical power consumption, i.e., to produce a more efficient injector apparatus and a correspondingly more efficient flotation device.
According to the present invention, the injector apparatus of the kind referred to above is characterized in that the outlet of at least one central air supply pipe disposed substantially concentrically with the constriction is arranged a short distance after the constriction, and in that the outlet of the mixing pipe is constructed similarly to a radial diffusor.
The injector apparatus of the present invention is generally designed for the stream of liquid to be supplied perpendicularly from above to the liquid which is to be aerated, and for the air intake zone to lie above the level of the liquid in the flotation tank. This results in the following advantages: the essential structural length of the injector apparatus requires no additional lateral space, as would be the case if the injector apparatus were to be fitted along side, for example, in the bottom of the container; this arrangement perpendicularly from above is suitable for a large injector, as no high pressure increase due to change of momentum in the mixing pipe is necessary; and with this arrangement there is no necessity to overcome the hydrostatic pressure due to the height of the liquid in the tank, since the same head of liquid is present in the mixing pipe. The production of a corresponding pressure increase by change of momentum in the mixing pipe would require an uneconomically high flow speed in the nozzle. Moreover, only a small amount of the flow energy has to be reserved in order to achieve a distribution of the gas bubbles in the tank. The flow speed necessary for this depends on the geometry and the diameter of the tank being aerated.
Again, because of the perpendicular arrangement of the injector apparatus in the tank, the use of a so-called radial diffusor is advantageous; in this case, the radial diffusor displays better properties than the conical straight diffusor which would otherwise normally be used. In the radial diffusor having suitable geometry, a considerable reduction of the flow speed, and thus a high increase in pressure, can be achieved with a short structural length, and a high level of efficiency. In addition, desired radial flow and distribution of bubbles in the tank are produced thereby at the same time.
The amount of air sucked in is generally dependent on the flow speed at the narrowest point, thus in the nozzle or orifice, on the flow rate of suspension with the flow speed at the outlet from the mixing pipe, and also on the pressure prevailing there and on the geometry of the narrowest point, i.e., its diameter, and on that of the mixing pipe, and on the length of the latter.